Concrete roadway



1966 u. FINSTERWALDER 03 CONCRETE ROADWAY 5 Sheets-Sheet 1 Filed May 15, 1964 AGT u. FINSTERWALDER 3,286,603

Nov. 22, 1966 V CONCRETE ROADWAY 5 Sheets-Sheet 2 Filed May 15, 1964 w w @KH Q U ER CCCCCCCCCCCCC AY /NVENT 04/9/09 74492)? A105? United States Patent 3,286,603 CONCRETE ROADWAY Ulrich Finsterwalder, Munich-Obermenzing, Germany,

assignor to Dyckerholf & Widmann Kommanditgesellschaft, Munich, Germany Filed May 15, 1964, Ser. No. 367,760

Claims priority, application Germany, Mar. 16, 1959,

6 Claims. (Cl. 94-8) The present invention relates to improvements in concrete roadways and is particularly concerned with prestressed concrete roadway construction. More in particular, the invention relates to concrete roadways which are prestressed by means of continuous prestressed elements that compensate for expansion and contraction resulting from differences in temperature. Elements of the type utilized in roadways in accordance with the present invention are similar to the elements disclosed in applicants US. application Serial No. 15,240 now Patent No. 3,156,169 and to the extent that the present invention incorporates features of the aforementioned earlier dis closure, the present disclosure is a continuation in part.

In the construction of concrete roadways, particularly the surface slabs of concrete, it is normally necessary to provide transverse gaps at predetermined distances due to the movement of the concrete resulting from differences in temperature. Such gaps always constitute weak points because the gaps interrupt the ri-gidness of the top of the concrete roadway. As a result an increased load of the bed occurs at the gap, and owing to the shaking of the ground caused by the rolling traffic, settling takes place which causes breaks in the roadway in the region of the gaps. As a result of the breaks moisture can enter, which then leads to softening of the ground. Further settling finally results in breaking and complete destruction of the concrete of the roadway which, beginning at the gaps, extends further and further into the roadway slab.

By using prestressing in the roadway slab it is possible to increase the distance of the gaps and thus reduce the number thereof. As a result of this, however, the expansion that has to be compensated for at the gaps increases, so that the gaps have to be equipped with the structural transfer means that are conventional in the construction of bridges. At any rate, the gaps remain as such. Besides, in the construction of roadway sections of great length considerable losses occur in the prestressing forces from the tensioning locations to the center of the slab owing, on the one hand, to the friction of the tensioning members in the covering sleeves and, on the other hand, to the friction of the roadway slab on the subsoil, so that there is merely a part of the initial prestressing force imparted to the anchoring which is effective in the center of the section. Finally, the frictional force between the roadway slab and the subsoil is an indefinite and variable factor, the effect of which can lead to rendering the prestressing in the central part of the section between the two gaps from which prestressing was effected insufficient to prevent the opening of the breaks in the event that they might form.

In accordance with the invention a new and different course is provided for overcoming the aforementioned difficulties in that prefabricated concrete elements are used which are preferably rod-like elements that are prestressed and disposed as the armoring of the roadway slab extending parallel and/ or at an angle to the longitudinal direction of the roadway and disposed at a distance from one another upon the subsoil, Where in each of the concrete elements one or more prestressing members are provided and the prestressed concrete bodies are disposed sequentially in rows and are connected at their ends to constitute an uninterrupted armoring.

3,286,603 Patented Nov. 22, 1966 In a preferred embodiment of the invention the prefabricated concrete bars are armored at their longitudinal center axis with a tensioning rod which is provided along a portion, preferably one-half of its circumference, with hot rolled ribs extending in a thread-like manner and along the side of the circumference that is opposite to these ribs with recesses which between them form ribs or lands of a height corresponding to the original surface of the rod.

The anchoring of the imparted tensioning or prestressin-g forces is effected in such a manner that at the ends of the concrete bars disk-like anchoring elements are disposed which are adapted to the cross-section of the bars and against which an anchoring nut of sleeve-like construction supports itself, which has recessed portions extending in thread-like fashion in the form of an internal thread that cooperate with the ribs of the tensioning rod onto which they can be threaded. The anchoring nut is provided at its outer circumference with a normal thread. The connection of the individual concrete bars may then be effected by threaded sleeves that are secured by means of lock nuts and which are screwed onto the anchoring nuts that are in threaded engagement with the rod ends that extend beyond the ends of the bars.

It is also possible in accordance with the invention to effect the connection of the concrete bars not by positive coupling means at their ends but by arranging the armoring bodies at their ends closely adjacent to one another in a longitudinally overlapping manner in accordance with overlap practices for armoring inserts which are conventional in steel concrete construction.

It is also advantageous to produce in the concrete roadway slab after the hardening of the concrete small notches that enter only to a slight depth and are arranged at predetermined distances transversely of the longitudinal direction of the roadbed and which extend over the entire width of the slab.

The important advantages of such a roadway slab are in the complete elimination of transverse gaps in the roadway, which is of extreme importance for the durability of a concrete roadway. The elimination of the gaps achieves, above all, that the subsoil to the extent that it has been evenly treated before the placing of the cover is evenly rocked in by the rolling trafiic in a manner that the continuous roadway slab can follow this movement without breakage.

While it was necessary in all concrete roadways known heretofore, whether they are armored, slightly armored, or prestressed structures, to place the greatest importance on a sliding surface between the slab and subsoil, the concrete roadway in accordance with the present invention is undisplaceably poured upon the subsoil and interdented therewith. As a result the wheel pressure that is distributed over a larger surface area by the rigid concrete slab can only enter the subsoil in a ray-like manner, whereby a compression force is formed besides the bending in the roadway slab below the load and which essentially reduces the bending stress force approximately to onehalf. As a consequence the slab in accordance with the invention can be constructed with less armoring or be made of smaller thickness while maintaining the same carrying capacity than the structures known heretofore.

A further advantage of economic nature is also provided in this connection by the elimination of the fine bedding and other provisions made for reducing the friction between the roadway slab and the ground by insertion of layers of paper and the like. Furthermore, the mortaring of the ground can be eliminated because due to the even load on the ground and owing to the elimination of the sliding layer, any additional fastening is not necessary.

Further advantageous features and details provided by the invention will become apparent from the following specification with reference to the embodiments of the invention illustrated in the accompanying drawings, in which FIG. 1 is a perspective view of a section of a roadway slab in accordance with the invention with the concrete elements in place;

FIG. 2 shows the end of a concrete element on a somewhat larger scale;

FIG. 3 is a partial section to a still larger scale illustrating the connection of two concrete elements; and

FIGS. 4 and 5 illustrate further examples of the arrangement of the concrete elements inside the roadway slab.

In the slab section illustrated in FIG. 1 prior to laying the concrete the interrupted edge lines are intended to indicate that the section may be continuous in all directions to any length without gaps. The roadbed slab 1 per se rests upon a plain surface 2 that is prepared in a known manner and is not further illustrated in the drawings. The thickness of the roadbed slab 1 is chosen in accordance with the static requirements. As a rule it is between 14 and 20 cm.

In the embodiment in accordance with FIG. 1 the concreate bars 3 which rest upon the subsoil surface 2 extend in the direction of longitude 4 of the roadway slab 1. As a rule they are displaced at equal distances from one another over the width of the roadway while each row of successive prestressed concrete bars extends over the entire length of the roadway slab to be constructed. Each of these rows thus consists of an optional number of prestressed concrete bars 3 arranged in sequence of round or multi-cornered, preferably square, cross-section with broken edges that are located directly upon the sub-soil or are somewhat embedded therein. Above these rows of prestressed concrete bars 3 there are arranged bars 5 which are of the same form of construction. In particular cases it is possible to provide in the transverse direction in a known manner an armoring of conventional reinforcement members in tubular coverings; finally it is also possible in some cases to provide armoring of loose, not prestressed steel rods.

In accordance with the invention the concrete bars 3 or 5 are armored by a tension member extending along their center axis. It is particularly advantageous if a particularly formed tension rod 6 is used which has helically extending hot rolled ribs 7 over a part thereof, for example, one-half of its circumference, which constitute parts of a thread. Along the side opposite that having the thread ribs 7 the tension rod 6 is provided with indentations 8 that are likewise produced by a rolling operation. The indentations also extend obliquely to the rod axis, and suitably in a manner that is opposite in direction to the partial thread formed by the ribs 7. The indentations 8 in turn cause lands or ribs 9 to form between them which correspond to the original surface of the rod.

This type of armoring rod provides primarily the advantage that a partial thread exists on one side of the rod which is formed by ribs, which on the one hand serves for screwing on suitably formed anchoring or connecting means, and which on the other hand, in combination with the indentations provided along the other rod side, makes it possible to statically use the armoring rod as ribbed steel. The indentations increase the adhesion effect of the steel rod in the concrete and thus establish as far as static characteristics are concerned the usability of the rod as ribbed steel, but do not interfere with the possibility of threading on connecting members since they engage the locations corresponding to the original rod surface that form ribs 9 between the indentations 8 and which, in a sense, have remained standing.

Each of the concrete bars has for an end closure a steel plate 10 which is generally in the form of a shell adapted to the cross-section of the concrete bars and which has a round aperture 19 for passing through the tension member. A steel plate or disk 10 of this type is provided at both ends of the concrete bar 3 so that the tension rod 6 extends through the aperture 19 beyond the disk 10. Tensioning nuts 11 or the like are provided for anchoring the prestressing forces that have been imparted. Such nuts are in the form of sleeves and have an internal thread 12 which as a whole corresponds only in part to the circumference of the thread illustrated. Thus these tension nuts 11 can be threadedly engaged with the projecting ends of the tensioning rods 6 and contact with one of their ends the disk 10 and in this manner form the anchoring means for the tensioning rod 6.

In order to provide a simple and practical possibility for connecting the individual concrete bars with one another the tensioning nuts 11 are provided with a complete normal thread 13 at their outer circumference. This thread 13 which may be cut or rolled on and where, contrary to the partial thread formed by ribs 7, the individual threads are closely together, provides the advantage that the threaded sleeve 14 which is used for connectig adjacent concrete elements 3 may be relatively short. For the purpose of preventing the unintentional loosening of the threaded sleeve 14, lock nuts 15 are provided at both ends of the sleeve.

The coupling of the concrete bars with one another is effected in a manner that the tension nuts 11 of the bars that are to be connected are first provided with lock nuts 15. Thereupon a connecting sleeve 14 is threaded onto one end over one-half of the length of the tensioning nut and is retained by the lock nut. By rotating the entire concrete bar 3 that has to be connected one-half of the tensioning nut 11 associated with that bar is now introduced in the threaded sleeve on the preceding element, and after threaded interengagement has been established it is held in the final position by tightening the second lock nut 15.

It is particularly advantageous in this connection that the tension rod used in accordance with the invention, and thereby also the concrete bars, can be produced in any desired lengths because the thread necessary for providing the anchoring or connecting means has been provided over the entire length of the anchoring rod. In order to effect a connection of the concrete bars 3 at their ends no special provisions need to be made in ac cordance with the invention to effect the anchoring or provide sleeve connections, for example, by providing threads upon the ends of the rods, but it is possible at any desired position of the armoring rod to have it project beyond the concrete body and then to thread onto these ends one of the anchoring means, such as a tensioning nut 11 that is provided with a suitable thread. In this connection the same ribs 7 which in combination with the concrete serve to increase the retention also serve as the thread.

The production of the individual concrete elements 3 or 5 can be effected in any desired manner. Thus they can be formed in situ in the tensioning bed so that the prestressed steel rod comes into immediate contact with the concrete. In that case the nut 11 serves only for the additional securing of the anchoring and for connecting the concrete elements at their ends. The concrete bars can, however, also be produced from prestressed concrete with subsequent connection or by interlinking prefabricated partial sections. Thus an armoring element 3 suitably comprises several prefabricated individual parts 3' of relatively short length, which along their center axis are provided with a tubular channel 16 by means of which they are drawn over the steel rod 6. At their front end 17 these partial elements 3 must then fit snugly against one another (see FIG. 1). At the end of a bar 3 the outer ends of the parts 3' then present the anchoring element 10. In lieu of a steel rod it is also possible to use bundles of thin tension rods or wires. For the better adhering of the concrete for the concrete element roadway slab poured in situ these may be provided with a rough surface or flat transverse grooves upon the surface.

The prestressing force imparted to the tensioning memher is selected to be relatively high, and after creeping and contracting of the concrete it should be 150 kg./cm.

The advantages obtained with the roadway covering in accordance with the invention are based on the following concepts: If it is assumed that the pretensioned or prestressed concrete elements 3 are embedded in concrete approximately at the average temperature of the year, then they retain their tension at that temperature while the concrete of the roadbed slab has imparted to it pulling or tension forces by the restraint at the ends thereof against shortening caused by contraction. As the ambient temperatures increase a compression force will develop because any heat expansion of the roadway slab is prevented by the ends. Thus a temperature increase of approximately 20 C. with a modulus of elasticity of the concrete of 300,000 kg./cm. will result in an increase in tension of 60 kg./cm. of the armoring elements embedded in the roadway slab by the prevention of the heat expansion, which causes the tension of the individual concrete element to increase to 210 kg./cm. and that of the surrounding concrete to 60 kg./cm less the tension resulting from shrinkage. As the temperature decreases by 20 C. the tension in the element will decrease from 150 kg./cm. to 90 kg./-cm. while the surrounding concrete of the concrete slab has imparted to it pull expansion of 0.2 mm./m. in addition to the expansion caused by the shrinking.

The prestressed concrete elements embedded in the roadway slab thus may have imparted thereto changes in length caused by dilferences in temperature without losing the ability of absorbing pushing or bending forces. Due to the high prestressing in the concrete elements there remain-s a suflicient pressure tension reserve for absorbing the bending forces caused by traflic load-s in the roadway slab. The local concrete of the slab which is not prestressed itself has a good connection with the surfaces of the concrete bars and, as the temperatures decrease and shrinking takes place, must retain its original length. This causes it to expand, and this expansion may exceed the known measure of expansion capacity of the concrete which is about 0.15 rum/m. Owing to this connection with the local concrete which is essentially better than in connection with normal reinforcing means, an expansion which is greater than 0.15 mm./m. will cause a reversible plastic expansion of approximately the same magnitude before a crack develops. Since with considerable difierences in temperature also this expansion capacity of the concrete is not yet sufiicient, cracks will at first develop at the average distance of 3 m. which are limited or attracted to these particular locations by the notching of the surface of the slabs in accordance with the invention. Inasmuch as transversely disposed tensioning members favor the forming of cracks, it is suit-able if such members are used to provide the notching above them.

In practice the construction of a roadway in accordance with the invention is efi'ected in such manner that after the armoring 3, '5 of a roadway section is placed in the described manner, the roadway slab 1 is poured and the concrete set, after the hardening of the concrete small notches 18 are produced at the top of the roadway slab at distances of about 3 m. and having a width of about 6 mm. and a depth of about 20 mm. which can be effected by means known in the art. It is, of course, also possible to produce these notches during the time the concrete of the roadway is poured by taking the proper measures.

Inasmuch as prestressed concrete bars impart a considerably greater capacity of expansion to the local concrete than it would have without this armoring, only small notches 18 will develop which will close under the load and will not decrease the bending resistance Olf the slab.

Owing to the small width of the cuts it is possible to forego the grouting that is normally required when there are gaps. The notches may be filled in with rock dust or also at the bottom of the notches addition-ally with an elastic coating which prevents the entrance of water. The cuts do not aifect the trafiic rolling over them in any manner whatsoever.

Having now described my invention with reference to the embodiment illustrated in the drawings, I do not wish to be limited thereto, but what I desired to protect by Letters Patent of the United States is set forth in the appended claims.

I claim:

1. Joint-less roadway of concrete comprising a concrete slab, prestressed armoring elements of concrete in the form of elongated bars or the like embedded in the slab and disposed generally parallel to the longitudinal direction of the roadway in spaced relationship alongside one another, each of said elements being provided at the longitudinal axis thereof with at least one prestressing member having projecting ends adapted to receive tensioning nuts, and a plurality of said prestressed concrete elements being disposed sequentially in rows with the ends thereof in force transmitting relationship to one another to constitute an uninterrupted armature.

2. Jointless roadway of concrete comprising a concrete slab, prestressed armoring elements of concrete in the form of elongated bars or the like embedded in the slab and disposed generally parallel to the longitudinal direction of the roadway in spaced relationship alongside one another, each of said elements being provided at the longitudinal axis thereof with at least one prestressing member, and a plurality of said prestressed concrete elements being disposed sequentially in rows with the ends thereof in force transmitting relationship to one another to constitute an uninterrupted armature, said prestressing member being a tensioning rod having rolled ribs forming a helical pattern on one side of substantially one-half the circumference of said rod and having on the side opposite the side having said rolled ribs indentations forming lands there-between, said :lands being of a height corresponding substantially to the original surface location of said rod.

3. Jointless roadway of concrete comprising a concrete slab, prestressed armoring elements of concrete in the form of elongated bars or the like embedded in the slab and disposed genera-11y parallel to the longitudinal direction of the roadway in spaced relationship alongside one another, each of said elements being provided at the longitudinal axis thereof with at least one prestressing member, and a plurality of said prestressed concrete elements being disposed sequentially in rows with the ends thereof in force transmitting relationship to one another to constitute an uninterrupted armature, said prestressing member being a tensioning rod having rolled ribs forming a helical pattern on one side of substantially one-half the circumference of said rod and having on the side opposite the side having said rolled ribs indentations forming lands therebetween, said lands being of a height cor-responding substantially to the original surface location of said rod, and disk-like anchoring members of a cross section adapted to the cross section of said bar disposed at the ends of the bar and an anchoring nut in the form of a sleeve in engagement with each said disk and having a recessed internal thread of helical configuration in threaded engagement with corresponding said ribs.

4. Jointless roadway of concrete comprising a concrete slab, prestressing armoring elements of concrete in the form of elongated bars or the like embedded in the slab and disposed generally parallel to the longitudinal direction of the roadway in spaced relationship alongside one another, each of said elements being provided at the longitudinal axis thereof with at least one prestressing member, and a plurality of said prestressed concrete elements being disposed sequentially in rows with the ends thereof in force transmitting relationship to one another to constitute an uninterrupted armature, said prestressing member being a tensioning rod having rolled ribs forming a helical pattern on one side of substantially one-half the circumference of said rod and having on the side opposite the side having said rolled ribs indentations forming lands therebetween, said lands being of a height corresponding substantially to the original surface location of said rod, and disk-like anchoring members of a cross section adapted to the cross section of said bar disposed at the ends of the 'bar and an anchoring nut in the iform of a sleeve in engagement with each said disk and having a recessed internal thread of helical configuration in threaded engagement with corresponding said ribs, said anchoring sleeve having an external conventional thread for receiving threaded connecting members operative to connect ends of adjacent said bars.

5. Jointless roadway of concrete comprising a concrete slab, prestressed larmoring elements of concrete in the form of elongated bars or the like embedded in the slab and disposed obliquely to the longitudinal direct-ion of the roadway in spaced relationship alongside one another, each of said elements being provided at the longitudinal axis thereof with at least one prest-ressing member having projecting ends :adapted to receive tensioning nuts, and a plurality of said prestressed concrete elements being disposed sequentially in rows with the ends thereof in force transmitting relationship to one another to constitute an uninterrupted armature.

6. Jointless roadway of concrete comprising a concrete slab, prestressed armoring elements of concrete in the form of elongated bars or the like embedded in the slab .and disposed obliquely to the longitudinal direction of the roadway in spaced relationship alongside one another, each of said elements being provided at the longitudinal axis thereof with at least one prestressing member, and a plurality of said prestressed concrete elements being disposed sequentially in rows with the ends thereof in force transmitting relationship to one another to constitute an uninterrupted armature, said prestressi-ng member being a tensioning rod having rolled ribs forming a helical pattern on one side of substantially one-half the circumference of said rod and having on the side opposite the side having said rolled ribs indentations forming lands therebetween, said lands being of a height corresponding substantially to the original surface location of said rod, and disk-like anchoring members of a cross section adapted to the cross section of said bar disposed at the ends of the bar and an anchoring nut in the form of a sleeve in engagement with each said disk and having a recessed internal thread of helical configuration in threaded engagement with corresponding said ribs, said anchoring sleeve having an external conventional thread for receiving threaded connecting members operative to connect ends of adjacent said bars.

References Cited by the Examiner UNITED STATES PATENTS 2,552,364 5/1951 Bradberry 52-738 3,066,581 12/1962 Goldbeck 94-8 FOREIGN PATENTS 871,681 1/1942 France. 711,449 6/ 1954 Great Britain.

CHARLES E. OCONNELL, Primary Examiner.

N. C. BYERS, Assistant Examiner. 

1. JOINTLESS ROADWAY OF CONCRETE COMPRISING A CONCRETE SLAB, PRESTRESSED ARMORING ELEMENTS OF CONCRETE IN THE FORM OF ELONGATED BARS OR THE LIKE EMBEDDED IN THE SLAB AND DISPOSED GENERALLY PARALLEL TO THE LONGITUDINAL DIRECTION OF THE ROADWAY IN SPACED RELATIONSHIP ALONGSIDE ONE ANOTHER, EACH OF SAID ELEMENTS BEING PROVIDED AT THE LONGITUDINAL AXIS THEREOF WITH AT LEAST ONE PRESTRESSING MEMBER HAVING PROJECTING ENDS ADAPTED TO RECEIVE TENSIONING NUTS, AND A PLURALITY OF SAID PRESTRESSED CONCRETE ELEMENTS BEING 